Means for protecting electric conductors.



NO. 771,307. PATENTED OCT. 4, 1904.

E. M. HEWLETT. MEANS FOR PROTECTING ELECTRIC OONDUGTOBS.

APPLIGATION FILED THE. 9. 1903.

Fig. 1.

N0 MODEL.

Wrifnesses. lnvenLor. 2'", i550 $4M. fidwardmfiewlefit 6 W WW V UNITEDSTATES Patented October 4, 1904.

PATENT OEEIcE.

EDWARD M. HEWVLETT, OF SOHENEOTADY, NEW YORK, ASSIGNOR TO GENERALELECTRIC COMPANY, A CORPORATION OF NET/V YORK.

ELECTRIC CONDUCTORS.

SPECIFICATION forming part of Letters Patent No. 771,307, dated October4, 1904;.

Application filed February 9, 1903.

To all whmn it may concern:

Be it known that 1, EDWARD M. HEWLETT, a citizen of the United States,residing at Schenectady, county of Schenectady, State of New tricConductors, of which the following is a specification.

The present invention relates to protector devices for electricalapparatus, and more particularly to devices for preventing thedestructive effect of reactive discharges in inductive circuits.

The common practice for protecting electrical apparatus against abnormalor injurious currents of electricity consists in providing devices inthe conductors which suddenly interrupt the current when it exceeds acertain volume or tension; but where there is considerable inductance inthe circuit the sudden interruption of the current by these protectordevices gives rise to very powerful reactive discharges in the form ofsparks which jump across contiguous portions of the circuit and rupturethe insulation.

The object of my invention is to provide means for automatically closingan inductive circuit through an auxiliary path of considerableresistance at the time or just before the main conductor-circuit isinterrupted, as in the case of burning out of a fuse, to thereby preventinjury to the. insulation by the destructive discharges of the inducedcurrent.

The invention will be more readily understood by reference to theaccompanying drawings, forming a part of this specification, in WhichFigure l is a conventional representation of an-exciter-circuit for analternating-current machine provided with one form of protector deviceembodying my invention. Fig. 2 is a similar View with the circuitprovided with another form of protector device, and Figs. 3 and 4 aredetails to be hereinafter referred to.

In the arrangement shown in the drawings the inductive conductor to beprotected is that carrying the exciting-current of the field of thealternating-current machine A (indicated at 1) and having the leads 2and 3 to the ex- Serial No. 142,466. (No model.)

citer B. As shown in Fig. 1, the lead 3 is provided with a thermalcut-out or fuse L, and located in proximity thereto, but out ofimmediate contact, is a metallic finger 5, connected through the shuntor auxiliary resistance-conductor 6 to lead 2. The finger 5 may bebifurcated, as shown in Fig. 42, so that it will extend across bothsides of the fuse and is supported by a shank 5, which is arranged inproximity to a binding-post of the fuse. The fuse i is shown with itscross-section reduced at its middle to insure its initial rupture atthat point, and the metallic finger 5 is positioned directly oppositethat point, so that a part of the arc will jump to the fingersubstantially at the instant of its formation and automatically completea circuit through the auxiliary conductor 6. The action of the finger 5would be substantially the same if it were somewhat removed from therestricted portion of the fuse, as shown in Fig. 3, for as soon as thefuse melts an arc is at once formed which envelops the finger andcompletes the circuit through the auxiliary conductor 6. The shank 5 ofthe finger, by means of its location in proximity to the fusebinding-post, provides an arcing-surface, so that the current mayreadily arc across the intervening space after the fuse has been burnedaway.

In the arrangementshown in Fig. 2 a switchblade 7 is provided forpositively and automatically closing the circuit through the auxiliaryconductor 6 upon the blowing of the fuse 4:. The switch 7 is connectedto one leadwire 3 through its pivoted support 8 and the other lead-wire2 by means of the fuse 4:, secured at its ends to the free end of theswitchlever and to a terminal contact 9, carrying the binding-post forthe lead-wire 2. The switch-lever 7 is normally pressed away from thecontact 9 by a spring 10 and is adapted to close automatically thecircuit through the auxiliary circuit 6 by means of an integralprojection 11 therefrom coming into engagement with the terminal contact12 of the circuit 6 when the free end of the switch-lever is released bythe blowing of the fuse &. lVhen the fuse blows, the current will arcacross between the ruptured ends of the fuse until the switch-lever 7has moved far enough to bring its projection 11 into engagement with thecontact 12, thereby completing the field-circuit through theresistance-conductor 6 before the main exciter-circuit is broken.

If no resistance were inserted in the auxiliary conductor 6, the exciterwould short-circuit itself therethrough unless the breaking of theexciter-circuit were simultaneous with the closing of the field-circuitthrough the auxiliary conductor 6.

My invention is capable of a variety of applications, and it is in noway restricted to the particular arrangements shown in the drawings.

What I claim as new, and desire to secure by Letters Patent of theUnited States, is-

1. The combination with an electric circuit having inductance in asection thereof, of means for breaking said circuit between saidinductance-section and its source of excitation, and means forautomatically closing the inductance portion of said circuit uponitself.

2. The combination with an electric circuit having inductance in asection thereof, of means for breaking said circuit between its sourceof excitation and said inductance-section, and means for automaticallyclosing the inductance portion of said circuit upon itself throughresistance.

3. The combination with an electric circuit having inductance in asection thereof, of a fuse for breaking said circuit between its sourceof excitation and said inductance-section, and means for automaticallyclosing the inductance-section of said circuit upon itself upon theblowing of the fuse.

i. The combination with a field-circuit conductor and its exciter, of athermal cut-out located in one side of said circuit, and a terminalfinger located in proximity to said cutout and connected by aresistance-conductor to the opposite side of said circuit.

5. The combination with a field-circuit conductor and its exciter, of athermal cut-out located in one side of said circuit, a normally inactivecircuit connected at one end to the opposite side of said circuit, and aterminal finger connected to the other end of said normally inactiveconductor and located in proximity to said cutout and adapted to beenveloped by the arc formed upon rupture of the cut-out therebycompleting a path for the reactive discharge.

In witness whereof I have hereunto set my hand this 7th day of February,1903.

EDWARD M. HEWLETT.

Witnesses:

BENJAMIN B. HULL, HELEN ORFORD.

